Spirit Barn
The Spirit Barn is a place where spirits that are not being kept in your Medallion can be stored. It is also where you can hatch Spirit Eggs. You can unlock the blueprint for the spirit barn by completing the Quest "Spirit Research: Taming Spirits 101". When the quest is completed, upon waking up the next day, you will receive a letter from Zed containing the blueprints for the Spirit Barn, Spirit Stall, and Spirit Nest.
To build a Spirit Barn, use the Moonstone Enchanter. You will need 100 wood, 100 stone, 3 Iron Ingots, and 1 Moonstone Ingot. There is no crafting time, and the item is made instantly. It can be placed anywhere, but similarly to the Alchemist Tent, it can't be moved until another one is placed and exists elsewhere in the world.
When built, the Spirit Barn will automatically contain 1 Spirit Stall. If you want any more Spirit Stalls or Spirit Nests, you must build those from the Moonstone Enchanter.
Paolo sells Spirit Barn upgrades at their Workshop that increase the maximum number of Spirits you can keep in the Barn.